I believe I have the key to the origin of this expression. Previous postings suggest jousters on horseback with lances/tilting at windmills. Intuitively wrong as weapon involved which makes no sense. So, I disagree with that line of thinking and suggest looking at horse gaits instead. The Icelandic horse, brought to Iceland by Vikings, has gaits as follows: walk, trot, tolt (with an umlaut, pron: 'toelt'), canter, pace. The tolt was bred out of horses on Europe's mainland. It is a gait faster than trot and far more comfortable for the rider. Ridden sitting back in saddle as per sitting trot -- no posting (rising) involved as in fast trot to miss alternate beats. 'Normal' horses can be taught to tolt but it does not come naturally. So, any contributors with knowledge of gaits and germanic/scandinavian languages out there? Grateful your opinion on this.

I had always imagined the meaning of full tilt to be rather straight forward. I assumed the "tilt" referred to a forward lean or incline. If you lean forward you will reach a point where you have to move forward in order to prevent toppling over. The further you tilt, the faster you will need to go. At some point you reach "full tilt"...which is the speed required to counter-act the greatest slant you can achieve without planting your face. At least, that's the way I'm inclined to think. I just noticed this little "Easter Egg"... if you type "tilt" into Google the page is displayed at a slight angle. It took me a second or two to make the connection.

As you have said, the tölt is only really found among Icelandic horses and related breeds, although similar "ambling" gaits are found with other breeds.

The speed can vary considerably, but at its fastest, it approaches a canter, and certainly does not reach the speeds achieved with a gallop. And therein lies the problem for me. "Full tilt" means at the fastest possible pace. Even Icelandic horses who are capable of the tölt would change their gait to a canter or gallop to reach faster speeds. Don't get me wrong, a horse up to speed with a tölt gait would have more than enough speed up to give me the willies, but it is far from flat out.

As far as German is concerned, the term "Tölt" is used, but seems to me to have been loaned back from Icelandic and only refers to the Icelandic ambling gait. According to Wikipedia, the Old High German "celtari" was used for a gaited horse, and from this come both "tölt" in Icelandic and "Zelter", which is an antiquated German term for a gaited horse.

I have not looked around too much, but most of the explanations I have seen go along with what trolley said above. Explanations relating to jousting (tilting) appear to me to be suspect, as the word "tilt" refers more to the competition than the actual combative action. It has been suggested that the word actually derives from the barrier of coarse cloth separating the combatants, in which case it is cognate with the German "Zelt", a tent or an awning.

So yes, I agree with you that the jousting explanation makes little sense. The lance is only tilted during the approach and lowered to the horizontal when the combatants clash at full speed.

But I did love the Youtube clip of a tölt. Remarkable how still the rider is, but plenty fast enough to give me the willies.